Maize breeders have been crossing inbred parent lines, one acting as a male and one as a female to form hybrid seed. The process of developing inbred parent lines which are substantially homozygous usually required a hybrid cross to be selected and self-pollinated (selfed) for numerous generations to become nearly homozygous. This was a time consuming and expensive process. To shorten the time to develop homozygous inbreds in maize, maize breeders have been using a process of using a haploid inducer line to induce haploid seed on a hybrid parent. The chromosomes of the haploid plants are doubled to form double haploid homozygous inbred lines.
A high haploid induction rate allows a higher frequency of haploid seeds to be formed on the parent plant of interest. The parent plants can be pre-screened with genetic markers associated with desired traits or phenotypic observed traits to enrich the genetic potential of the parent plants. When these desired parent plants are pollinated by a haploid inducer that has a higher haploid induction rate, a higher potential of desired doubled haploids can be obtained with the desired genotype and phenotype.
Although the doubled haploid process resulted in faster production of homozygous inbreds, the volume of doubled haploid inbreds that could be produced was limited. The inducer lines had a low frequency of induction of haploids. A number of known haploid-inducing maize lines exist including but not limited to: stock 6, MHI (Moldovian Haploid Inducer), indeterminate gametophyte (ig) mutation, KEMS, RWK, ZEM, ZMS, KMS. The standard inducer lines such as Stock 6 were inducing only 1-3% haploid seeds. Induction of haploids was a rate limiting step in the process of producing doubled haploid lines.
Haploid induction (HI) is a class of plant phenomena characterized by loss of the male inducer chromosomes during embryo development. WO2012/030893 describes a slightly different region of chromosome (1) that is found responsible for haploid induction. The identified markers in the region responsible for haploid induction and increased haploid induction was described as being between 48,249,509-51,199,249 which is associated with a public marker umc1169 that has the physical position of (60,213,661). This region apparently aligns with the Haploid Induction region in Stock 6. Dong et al. (2013) Theor. Appl. Genet. 126: 1713-1720 describe a QTL located in bin 1.04 which explains up to 66% of the genotypic variance for haploid induction rate.
Haploid induction has been observed in numerous plant species, such as sorghum, rice, and other grasses. The HI appears to be a result of rearrangements of, mutations in, and/or recombinations, insertion, or deletions within a region of chromosome 1. Purported HI-lines have been studied and roughly identified. However, experimental evidence demonstrating a causative genetic agent of HI in maize has not been presented. Nor have the markers listed herein that associate with this trait been previously identified.
The presently disclosed subject matter provides isolated cDNA. In some embodiments, the isolated cDNA are selected from the group consisting of: (a) a nucleic acid having at least 90% identity to SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53; (b) a nucleic acid having at least 95% identity over nucleotides 91-1452 of SEQ ID NO: 33; (c) a nucleic acid that is the reverse complement of either of (a) or (b); and (d) a nucleic acid that encodes a polypeptide comprising an amino acid sequence that is at least 95% identical to SEQ ID NO: 54, or SEQ ID NO: 55, or SEQ ID NO: 56, or SEQ ID NO: 57 optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 54, or SEQ ID NO: 55, or SEQ ID NO: 56, or SEQ ID NO: 57.
In other embodiments, a synthetic hairpin nucleic acid construct comprising between 15 and 1000 nucleotides from SEQ ID NO. 33, 37, 52 or 53 and the antisense-complement thereof, such that the first and the second polynucleotide sequences hybridize when transcribed into a ribonucleic acid to form the hairpin-like double stranded ribonucleotide molecule. In further embodiments, the synthetic hairpin nucleic acid construct is selected from the group consisting of SEQ ID NO: 60 and SEQ ID NO: 61.
In other embodiments, an expression cassette for RNAi comprises a promoter operably linked to the synthetic hairpin. In further embodiments, the promoter is a constitutive promoter, optionally a maize ubiquitin-1 promoter, a rice actin-1 promoter, a rice ubiquitin-3 promoter, a rice alpha tubulin (tubA1) promoter, a cauliflower mosaic virus (CaMV) 35S promoter, a cestrum yellow leaf curling virus (CmYLCV) CMP promoter, a super MAS promoter, a sorghum ubiquitin-3 promoter, or a sugarcane ubiquitin-4 promoter. In other embodiments, the promoter is a stamen-, anther-, and/or pollen-specific promoter, optionally selected from the group consisting of SEQ ID NO: 58, a Triticum aestivum P19 promoter, a maize B200 promoter, a maize prCDPK-01 promoter, a maize prCDPK-02 promter, a rice alpha-N-acetylglucosaminidase (prOsANG) promoter, a rice MADS box gene promoter (optionally a prOsMADS1 promoter, a prOsMADS2 promoter, a prOsMADS6 promoter, a prOsMADS14 promoter, or a prOsMADS16 promoter), a rice anther specific-promoter (optionally a prRA8 promoter or a prOsG6 promoter). In other embodiments, the expression vector may optionally comprise a terminator. In further embodiments, the terminator may be SEQ ID NO: 59. In some embodiments consist of a plant comprising hairpin nucleic acid construct of the previous embodiments. This plant could be a monocot such as a maize plant.
Some embodiments consist of a method of creating a new haploid inducer plant with a silenced patatin-like phospholipase 2A, comprising transcribing a polynucleotide sequence capable of silencing the patatin-like phospholipase 2A, wherein said polynucleotide sequence is selected from the group consisting of: a polynucleotide sequence comprising the nucleic acid sequence set forth in SEQ ID NOs 33, 37, 52, 53 or the complement thereof, a functional fragment comprising at least 15 contiguous bases of any one of SEQ ID NOs 33, 37, 52, 53 or the complement thereof, a polynucleotide sequence having at least 95% sequence identity as determined using the BLASTN alignment tool to the nucleic acid sequence set forth in any one of SEQ ID NOs 33, 37, 52, 53 or the complement thereof, and a double-stranded ribonucleotide sequence produced from the expression of a polynucleotide sequence of any one of the above polynucleotide sequences, wherein silencing of the patatin-like phospholipase 2A creates a new haploid inducer plant.
Other embodiments are a plant made by the above method. The plant may be a maize plant or other monocot. Other embodiments are a method of inducing haploid embryos by using the pollen of the plant made by the above method to fertilize another plant, wherein the fertilization induces haploid embryos. Other embodiments are a method of identifying a maize plant that comprises a genotype associated with an increased haploid induction phenotype, comprising: isolating DNA from a maize plant, providing a reaction mixture comprising the DNA from a maize plant, the pair of primers comprising SEQ ID NO: 64 and SEQ ID NO 65 wherein the first primer is complementary to a sequence on the first strand of the target DNA and the second primer is complementary to a sequence on the second strand of the target DNA, Taq polymerase, and a plurality of free nucleotides comprising adenine, thymine, cytosine and guanine; heating the reaction mixture to a first predetermined temperature for a first predetermined time to separate the strands of the target DNA from each other; cooling the reaction mixture to a second predetermined temperature for a second predetermined time under conditions to allow the first and second primers to hybridize with their complementary sequences on the first and second strands of the target DNA, and to allow the Taq polymerase to extend the primers; and repeating steps (b) and (c) at least 20 times, wherein an amplification product of about 822 nucleotides indicates a maize plant that comprises a genotype associated with an increased haploid induction phenotype.
Some embodiments consist of an expression cassette for expression of a fertility restoring polypeptide in a plant, the expression cassette comprising an isolated nucleic acid of SEQ ID NO. 33 or 52 operably linked to a promoter that regulates transcription of the isolated nucleic acid of SEQ ID NO. 33 or 52 in a plant cell and/or tissue of interest, wherein the isolated cDNA of claim 1 encodes an amino acid sequence that is at least 95% identical to SEQ ID NO: 54 or 55, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 54 or 55.
Other embodiments consist of a kit for detecting the presence of absence of a HI-inducing allele in a plant, the kit comprising one or more nucleic acid- and/or amino acid-based reagents derived from the maize HI locus or from a locus linked thereto wherein the one or more nucleic acid- and/or amino acid-based reagents are designed to be employed in a nucleic acid- and/or amino acid-based assay for the presence or absence in the plant of: a nucleic acid having at least 90% identity to SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 33; a nucleic acid having at least 95% identity over nucleotides 91-1452 of SEQ ID NO: 33; a nucleic acid that is the reverse complement of either of (a) or (b); and/or a nucleic acid that encodes a polypeptide comprising an amino acid sequence that is at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57 optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57, or nucleic acid comprising nucleotides 1230-1233 of SEQ ID NO: 53.
In some embodiments, the isolated nucleic acids are selected from the group consisting of: a sequence having at least 90% identity to the listed SEQ ID NOs which comprise at least one sequence evidencing an association with a haploid inducing trait by its presence or absence selected from the group consisting of genes identified as GRMZM2G305400, GRMZM2G082836, GRMZM2G382717, GRMZM2G120587, GRMZM2G471240, GRMZM2G866758, and GRMZM2G003530.
The presently disclosed subject matter also provides expression cassettes for expression of the gene products made by the gene which is absent in HI plants. In some embodiments, an expression cassette of the presently disclosed subject matter comprises a nucleic acid sequence as described herein as a synthetic hairpin nucleic acid construct comprising between 15 and 1000 nucleotides from SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53 (such as, but not limited to SEQ ID NO: 60 or 61) operably linked to a promoter that regulates transcription of the isolated nucleic acid in a plant cell and/or tissue of interest, and/or an organelle or subcellular structure thereof. In some embodiments, the isolated nucleic acid present in the expression cassette encodes an amino acid sequence that is at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57. In some embodiments, the promoter is a native promoters associated with the genes within this haploid induction region (such as, but not limited to SEQ ID NO: 58). In some embodiments, constitutive promoter, which can optionally be selected from the group consisting of the native promoter, a constitutive promoter such as ZmUbi1, ZmUbi158, ZmUbi361, SbUbiCh3, SbUbiCh4, a maize ubiquitin-1 promoter, a rice actin-1 promoter, a rice ubiquitin-3 promoter, a cauliflower mosaic virus (CaMV) 35S promoter, a sorghum ubiquitin-3 promoter, or a sugarcane ubiquitin-4 promoter, or a promoter that is pollen specific. Examples of pollen promoters are shown in the art in pollen-specific expression cassettes. Pollen-specific genes have been described for maize (Lopez I, Anthony, R. G., Maciver, S. K., Jaing, C.-J., Khan, S., Weeds, A. G., Hussey, P. J. (1996). Pollen specific expression of maize genes encoding actin depolymerizing factor-like proteins. Proc Natl Acad Sci USA 93:7415-7420.) Such information can be used to identify other maize pollen-specific genes, and promoters and produce pollen-specific expression cassettes. In some embodiments, the expression cassette further comprises a transcription terminator operably linked to the promoter and/or coding sequence. Some embodiments are a promoter for anther, stamen or pollen specific expression comprising SEQ ID NO:58.
In some embodiments, the plant cell and/or tissue of interest is selected from the group consisting of a stamen cell, a microspore, a meiotic cell, a cell that differentiates into a stamen cell or a progeny cell thereof, an anther cell, a cell that differentiates into an anther cell or a progeny cell thereof. In some embodiments, the organelle or subcellular structure of the plant cell and/or tissue of interest is a microspore. Thus, in some embodiments, the promoter is a stamen-, anther-, and/or pollen-specific promoter, which in some embodiments is selected from the group consisting of a Triticum aestivum P19 promoter, a maize B200 promoter, a maize prCDPK-01 and prCDPK-02 promoter, a rice α-N-acetylglucosaminidase (prOsANG) promoter, a rice MADS box gene promoter (including, but not limited to a prOsMADS1 promoter, a prOsMADS2 promoter, a prOsMADS6 promoter, prOsMADS7 promoter a prOsMADS14 promoter, or a prOsMADS16 promoter), a rice anther-specific promoter (such as, but not limited to a prRA8 promoter or a prOsG6 promoter), a rice stamen-specific promoter (such as, but not limited to the promoters disclosed in U.S. Pat. No. 5,639,948); and a corn stamen-specific promoter (such as, but not limited to the promoters disclosed in U.S. Pat. No. 5,589,610). In some embodiments, the promoter is a promoter that is transcriptionally active in a plant mitochondrion. Exemplary such promoters include, but are not limited to those disclosed in Fey & Maréchal-Drouard, 1999 and Binder et al., 1996.
In some embodiments, the expression cassette further comprises a transcription terminator, optionally a Nos or ags terminator.
In some embodiments, the expression cassette further comprises a targeting peptide (TP) coding sequence that is operably linked to and in frame with a sequence that encodes an amino acid sequence that is at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57.
The presently disclosed subject matter also provides vectors comprising an expression cassette as disclosed herein.
The presently disclosed subject matter also provides transgenic plant cells comprising the presently disclosed expression cassettes, as well as plants, plant parts, and seeds comprising or derived from the presently disclosed transgenic plant cells.
The presently disclosed subject matter also provides isolated polypeptides comprising amino acid sequences that are at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57. In some embodiments, wherein the percent identity is calculated over the entire length of SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57. In some embodiments, the isolated polypeptides comprise amino acid sequences that comprise all or substantially all of amino acids 1-429 of SEQ ID NO: 54 locus.
The presently disclosed subject matter also provides subsequences, amplicons, and informative fragments of SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, as well as allelic variations thereof, wherein the subsequences, amplicons, informative fragments, and/or allelic variations can be used to identify the presence or absence of an allele associated with HI in a plant, or plant tissue, or plant cell.
The presently disclosed subject matter also provides compositions comprising amplification primer pairs capable of amplifying plant nucleic acid templates to generate marker amplicons, wherein the marker amplicons correspond to markers comprising informative subsequences of any of SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, or of the listed SEQ ID NOs. from this 0.6 MB region which comprise at least one sequence evidencing an association with a haploid inducing trait in this by its presence or absence selected from the group consisting of genes identified as GRMZM2G305400, GRMZM2G082836, GRMZM2G382717, GRMZM2G120587, GRMZM2G471240 (two), GRMZM2G003530, and GRMZM2G866758 (two) wherein the informative subsequences permit identification of the presence or absence of an allele associated with HI in plants. In some embodiments, the amplification primers are designed to amplify a subsequence of SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53 (exemplary primers, but not limited to SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66 or SEQ ID NO: 67). The presently disclosed subject matter also provides methods for producing plants that exhibit a new or increased HI trait. In some embodiments, the methods comprise (a) transforming a plant cell with an expression cassette comprising a nucleic acid as disclosed herein to produce a transformed plant cell; and (b) generating a plant from the transformed plant cell.
The presently disclosed subject matter also provides methods for identifying the presence or absence of allele associated with HI in plants. In some embodiments, the methods comprise (a) obtaining a sample from the plant comprising genomic and/or nuclear DNA and/or an RNA product derived therefrom; (b) contacting the sample with a pair of primers that, when used in a nucleic acid amplification reaction with a nucleic acid sample from the plant, produces an amplicon that can be used to identify the presence or absence of an allele associated with HI; (c) amplifying a fragment from said sample using the primer pair of (b), wherein the primer pair is complementary and binds to the nucleotide sequence of (b); and (d) detecting an amplicon that can be used to identify the presence or absence of an allele associated with HI in the plant.
The presently disclosed subject matter also provides methods for introgressing HI-inducing nucleotide sequences or haplotypes into plants. In some embodiments, the methods comprise crossing a first plant with a second plant to produce a third plant, wherein the genome of the first plant or the second plant comprises a nucleic acid sequence (in some embodiments a recombinant nucleic acid sequence) encoding a HI-associated gene product of the presently disclosed subject matter and selecting those plants that do not exhibit production of the gene product, or a gene product at substantially reduced levels. In some embodiments, the methods further comprise assaying the genome of the third plant for the presence or absence of the nucleic acid sequence (in some embodiments, the recombinant nucleic acid sequence) encoding the HI-associated gene product. A HI-associated gene product, can be a negative or positive association. In this instance the association is a negative association, i.e. the presence of the gene product is associated with the absence of the haploid induction trait. In some embodiments, the recombinant nucleic acid comprises SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, and/or encodes a polypeptide that is at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57. In some embodiments, the genome of the third plant that is assayed is the third plant's genome.
The presently disclosed subject matter also provides methods for selecting F0 parental plants predicted to produce haploid inducing plants that exhibit inducible HI traits. In some embodiments, the methods comprise identifying in the genome of an F0 plant the present or absence of a nucleic acid comprising a nucleotide sequence selected from the group consisting of: (a) a nucleic acid having at least 90% identity to SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 33, SEQ ID NO: 37, SEQ ID NO: 52 or SEQ ID NO: 53; (b) a nucleic acid having at least 95% identity over nucleotides 1-1452 of SEQ ID NO: 33; (c) a nucleic acid that is the reverse complement of either of (a) or (b); and (d) a nucleic acid that encodes a polypeptide comprising an amino acid sequence that is at least 95% identical to SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57, optionally wherein the percent identity is calculated over the entire length of SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56 or SEQ ID NO: 57.
In some embodiments, the methods comprise identifying in the genome of an F0 plant the present or absence of a nucleic acid comprising a nucleotide sequence selected from the group consisting of the listed SEQ ID NOs. 3, 9-46 from this 0.6 MB region which comprise at least one sequence evidencing an association with a haploid inducing trait in this by its presence or absence selected from the group consisting of genes identified as GRMZM2G305400, GRMZM2G082836, GRMZM2G382717, GRMZM2G120587, GRMZM2G471240 (two), and GRMZM2G866758 (two) wherein the nucleic acid has at least 90% identity to the selected SEQ ID NO. optionally wherein the percent identity is calculated over the entire length of the selected SEQ ID NO.
Thus, it is an object of the presently disclosed subject matter to identify and/or introgress and/or provide nucleic acids for inducing and/or inhibiting the HI trait in a plant.